Imogen: Last night when I was sleeping then there was lots of ambulances and firetrucks and school buses.
Me: Oh yes, I heard the sirens too. I didn't know there were school buses though.
Imogen: Oh yes, lots of school buses.
Me: Did you see them out your window?
Imogen: No, Mum. I heard their sirens going wooo-wooo. That was how I knowed it was school buses and ambulances and firetrucks.